The present invention relates generally to the field of power generation and in particular to a new and useful liquid fuel-fired burner for a thermophotovoltaic (TPV) system.
TPV electric generator systems operate by converting photons generated by an incandescent emitter into electric current. A basic TPV electric generator includes a burner which receives and burns a fuel. The incandescent emitter forms the boundary of the combustion region of the burner. The emitter is heated by combustion to incandescence, thereby emitting photons which are converted to electric current by adjacent photovoltaic cells. The photon""s energy must exceed the bandgap energy of the photovoltaic cell to free an electron that can potentially contribute to an electric current. The bandgap energy is dependent on the type of photovoltaic cell, but typically it is in the near-infrared region of the electromagnetic spectrum. The current application uses GaSb photovoltaic cells which have a bandgap energy of 0.73 eV. The emitter temperature must exceed 2400xc2x0 F. so that sufficient photons exceeding the bandgap energy are generated, thereby producing an energy efficient system with a high power density. Typically, a filter is provided to boost energy efficiency by reducing the amount of photons below the bandgap energy of the photovoltaic cells. In addition, excess heat energy contained in the combustion effluent is recycled to pre-heat combustion air and further improve the system efficiency. As a result, preheated air temperatures at the burner may exceed 1000xc2x0 F.
Low-flow, diesel-fired burners have been developed commercially for a variety of heating applications. None of the known diesel-fired burners have the necessary geometry or are capable of withstanding a sufficiently high operating temperature for this TPV application. Further, no known burners can achieve the necessary rapid heat release and heat transfer required in this TPV application either.
It is an object of the present invention to provide a burner with high combustion efficiency and rapid energy transfer for use in a TPV system.
It is a further object of the invention to provide a burner which can operate using a variety of liquid and gaseous fuels.
Another object of the invention is to provide a burner that can withstand the very high operating temperatures found in TPV systems.
Accordingly, a compact, high-temperature, liquid fuel-fired burner is provided having a fuel distribution tube with at least one integrated swirl vane adjacent to at least one exit hole in the body of the distribution tube. The swirl vanes may be machined on the outer surface of the fuel distribution tube near the top end. A ceramic burner cap is connected to the upper end of the fuel distribution tube. A liquid or gaseous fuel is provided through a first fuel feed tube protruding through the distribution tube, thereby forming a burner assembly. The burner assembly fits into a burner sleeve which forces primary combustion air through a passage formed between the sleeve and the swirl vanes. A combustion chamber is connected to the burner above the burner cap and distribution tube.
An ignitor, that can be inserted through the sleeve, is used to initiate combustion of the fuel and air in a combustion chamber above the burner cap. The used combustion products are redirected down the outside of the combustion chamber and burner sleeve through a recuperator inlet. The combustion products may then be processed in a connected recuperator, if desired.
The first fuel feed tube has a small orifice at the burner end and means for vaporizing the fuel. Preferably, the tube may be heated using an internal heater that vaporizes the fuel. Alternatively, a start-up heat energy source may be used in conjunction with a control means for balancing and achieving a steady state of operation between the start-up heat energy and energy recuperated within the burner. Preferably, the start-up heat energy source is an internal heater within the burner structure. Additionally or Alternatively, the means for vaporizing the fuel may comprise a second feed tube adjacent the first feed tube and a pilot flame which may be controlled such that, once sufficient energy is recuperated, the burner may operate in a steady state.
Further, the first feed tube may surround the vaporization means so as to form a helical path connected the fuel supply. This set up may also incorporate a means for determining the temperature of the fuel, such as a thermocouple, to permit variable control of the vaporization means.
The fuel feed tube can include a cleaning needle and/or a thermocouple for determining the fuel temperature at the orifice for regulation of the heater. A temperature sensor may also be employed. Further, the burner sleeve may be slidably coupled to the distribution tube so as to allow variable control of the size of the annular passage.
The burner cap, the fuel distribution tube, and swirl vanes may be machined from a single article, preferably comprising either high-temperature metallic alloy or a ceramic.
The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its uses, reference is made to the accompanying drawings and descriptive matter in which a preferred embodiment of the invention is illustrated.